Recently, as represented by photovoltaic power generation systems and fuel cell systems, in the field of energy production, the development of distributed power sources have been active and accelerated for the practical applications. Further, a storage battery system configured to store electric power generated at a distributed power source and night-time electric power and discharge the stored electric power during the peak electric power demand to achieve energy leveling is about to be put into practical use.
FIG. 1 is a configuration diagram of a conventional islanded operating system. FIG. 1 shows one configuration example of energy management systems, such as HEMS (home energy management system) and BEMS (building energy management system), including a commercial power source, an electricity meter, a distributed power source, a load, and a controller. Distributed power sources establish a grid connection in accordance with the phase of a commercial power source. A photovoltaic power generation system capable of reverse power flow discharges electric power according to the amount of incident sunlight, and reverses the flow to the system when electricity is generated in an amount equal to or larger than the load, so that the electricity can be sold (Japanese Patent Application Publication No. 2009-131056).
Moreover, a fuel cell system incapable of reverse power flow is managed to consume generated electric power using a load, while a storage battery system is managed to store extra electricity from distributed power source and discharge the electricity so that the energy can be used efficiently.
Further, for a blackout, the output of each distributed power source is provided with an output dedicated to an islanded operation as disclosed in Japanese Patent Application Publication No. 2009-131056.
A distributed power source in FIG. 1 establishes a grid connection in synchronism with a commercial voltage. Hence, when a commercial power source has a blackout, over-voltage, or over-frequency, the grid-connected operation is terminated. In addition, during a blackout, an islanded operation output (mainly single-phase two-wire AC distribution at 100 V) can be used at a socket which is provided to the distributed power source independently of the grid connection.
However, in order to use the islanded operation output during a blackout, a load device has to be connected to the dedicated socket of each distributed power source. Besides, the load device cannot be operated by the energy management that is optimal for receiving electricity from the commercial power source.
Furthermore, an islanded operation output with a CVCF (constant voltage constant frequency) inverter configured to perform PWM control has a larger load. When a non-linear load is connected, the voltage is greatly distorted, so that other distributed power sources are also adversely influenced.
The present invention provides an islanded operating system configured to disconnect from a commercial power source when the commercial power source fails, and capable of supplying a load with a low-distortion voltage source by an islanded operation.